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Community and Q&A

Best roof for PV panels

Karen Miller | Posted in Green Building Techniques on

We will be putting up Timberline GAF 30 roof shingles for a Net Zero new construction. Our builder wants to put them up now.. but should we first be putting up the PV solar panels brackets up first? And can you recommend web sites for beautifully installed PV panels? And if pretty much most of the FRONT side of the house (east roof) will be covered with PV panels.. do we need roof shingles underneath? Also open to a metal roof.. but too expensive!.. unless we can just do sections to hold the panels. Thanks for your advice!

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Replies

  1. Damon Lane | | #1

    Standing seam metal roof has the advantages that it will outlive the PV so you won't need to remove the panels while re-roofing, and that the panels can be quickly and waterproof-ly attached to the raised seams.

    Are you saying you are going to mount PV on an East facing roof? PV should roughly face the equator.

  2. Riversong | | #2

    The roof must be waterproofed before PV panels are installed. The most aesthetic installation is one that can't be seen (or hardly), such as as PV shingles or thin film PV adhered to a standing seam metal roof.

    If the panels are to be installed facing south on an east roof, then there's no way to make them look anything but obtrusive, since the panels will have to be angled toward the south.

    Roof mounted PV might offer better exposure, depending on the site, but requires water sealing the underlying roofing and wiring penetrating the roof. A much less obnoxious installation is a ground-level unit on a sun tracker, such as the excellent fully self-contained GPS/wireless controlled units from All Earth Renewables (All Sun Trackers).

    But, among the roof-mounting options, clamping to a standing seam roof is by far the best. I would invest in a durable roof before I would spend money on PV (net zero is a misguided goal for a house - extreme energy use reduction is a far more ecologically-responsible goal).

  3. J Chesnut | | #3

    Important questions here are who is responsible for the PV system to roof detail? who is responsible for installing it? and who is responsible if the roof leaks?
    Your builder wants to roof before the PV installation? Maybe they are trying to avoid liability. How can you roof before the installation and flash properly?
    Either the GC or the architect, in the interest of the client, needs to coordinate the proper roof install of a PV system. Be careful if the solar contractor isn't a sub of the GC.
    I've seen projects where the solar contractor was brought in by the architect or the client. It wasn't defined up front who would actually install the brackets to hold the PV panels and it therefore didn't appear in either the GCs bid for the solar contractors bid. You don't want to be in this scenario.

  4. A non mouse | | #4

    JChestnut... my neighbor has a non leaking solar install in snow country. Solar company said have your roof reshingled then they come in after no problem.

    And there has been no problem.

    again.. I have to mostly agree with RR though

  5. GBA Editor
    Martin Holladay | | #5

    Karen,
    1. If this is new construction, why is the PV array on the east side? Wouldn't it make more sense to design your house with a south roof?

    2. Although your title is "best roof for PV panels," it sounds as if you have already decided on using asphalt shingles, whether or not this choice is "best." That's OK -- shingles will work. But they won't last as long as standing-seam metal.

    3. If you want your PV array to be unobtrusive, the modules will probably be installed parallel to the roofing, with an air space of a few inches between the modules and the roofing. The air space is necessary and useful; it helps keep the modules cool.

    Of course, installing the modules parallel to the roofing won't really work on an east-facing roof.

    4. Your PV installer should definitely coordinate with your roofer. Your PV modules will probably be installed on aluminum rails that attach to brackets or pipes that need firm structural attachment. These brackets or pipes need to be flashed, and the flashing should be integrated with your shingle roofing.

  6. Karen Miller | | #6

    Thank you for your responses. Keep on hearing that standing seam is better than asphalt shingles. How long will the asphalt shingles last? We're looking at the 30 yr ones? And what's a good metal company to look at? Thanks again. Sorry.. meant to say South facing roof in my previous question.

  7. GBA Editor
    Martin Holladay | | #7

    Karen,
    Asphalt shingle warranties are marketing gimmicks, not predictions of service life. Most asphalt shingle roofs are replaced after 15 or 20 years. In many cases, the algae growth becomes so unsightly that homeowners replace their asphalt shingle roofs even sooner, for aesthetic reasons.

  8. Riversong | | #8

    I have to disagree with Martin once again. The warranties on asphalt shingle roofs almost exactly track the expected life and are generally proportional to the amount of material thickness.

    Most custom builders today are using what are called architectural shingles, or laminated shingles, both for the less uniform look and for the longevity. You can get shingles with up to 50 year warranties, but they'll cost you almost the same as a good standing seam metal roof.

    I don't know that the metal manufacturers are much different from each other in quality, but roofers will use different thicknesses of metal. Most roofers prefer 26g metal because it's easier to bend, but the better roofers use 24g which won't wrinkle like the thinner material but requires mechanical brakes in order to bend.

  9. Riversong | | #9

    I forgot to add that algae and moss growth on a shingled roof is usually secondary to organic debris collecting on the roof from nearby trees. With no trees, a steep roof slope and regular rain washing, there's generally no algae. The algae feeds on the debris and the moss feeds on the algae.

    You can get algae-resistant shingles that contain copper granules. Shingles are warrantied for up to 20 years against algae growth.

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